Adiponectin (also referred to as ACRP30 or GBP28) is a cytokine which is specifically produced and secreted mainly from adipose tissue, and is a protein consisting of 244 amino acids (see Non-patent Literature 1). It has been demonstrated that adiponectin has an effect of improving an insulin sensitivity, and an effect of accelerating fat burning in a liver and in a muscle. Since adiponectin has such effects, it is expected that normalization of the secretion of adiponectin will make it possible to comprehensively improve symptoms of metabolic syndrome such as high blood pressure, abnormal lipid metabolism, and diabetes (see Non-patent Literature 2).
As for diabetes which is one of diseases caused by metabolic syndrome, the Japanese Ministry of Health, Labor, and Welfare conducted an actual condition survey in 2006. According to the result of the survey: approximately 8.20 million people were strongly suspected of diabetes, and approximately 10.50 million people had an undeniable possibility of diabetes. That is, an estimated 18.70 million people in total were suspected of diabetes. It is said that people suffering from lifestyle-related diseases including diabetes and potential patients will increase, and what is important is to prevent such diseases by improving a lifestyle.
As described above, adiponectin relates to metabolic syndrome. Therefore, it is considered that adiponectin has a possibility of serving as an indicator of lifestyle-related diseases. Accordingly, it is considered that measurement of an in vivo concentration of adiponectin leads to maintenance of good health and to early detection of abnormal metabolism.
A concentration of adiponectin has been heretofore measured by an immunological measurement method in which used as an adiponectin-recognition material is an antibody which is a protein (the antibody is a monoclonal or polyclonal antibody obtained by using adiponectin as an immunogen) (see Patent Literatures 1 and 2). Specifically, Patent Literature 1 discloses a monoclonal antibody which makes it possible to measure a concentration of adiponectin as it is without modifying its natural structure, even though adiponectin is present in the forms of various multimers in blood. In addition, Patent Literature 1 discloses a testing method for Type 2 diabetes in which the monoclonal antibody is utilized. Patent Literature 2 discloses a polyclonal antibody which binds specifically with adiponectin. In addition, Patent Literature 2 discloses a reagent and a method for analyzing adiponectin in which reagent and method latex particles on which the polyclonal antibody is supported.
One of such immunological measurement methods is a sandwich technique utilizing an antibody. In the sandwich technique, specifically, a concentration of adiponectin is measured as below. First, an antibody specific to adiponectin is immobilized in a microplate. Then, a sample containing adiponectin is added thereto in order that adiponectin in the sample may react with the antibody. Adiponectin is thus immobilized in the microplate. Then, adiponectin thus immobilized is further reacted with another antibody which is labeled with an enzyme, a fluorescent compound, or the like, and which is different in epitope from the antibody immobilized in the microplate. Then, the enzyme or the fluorescent compound is detected so as to detect adiponectin.